Abstract:

Objective  This study investigates the circadian variation rules of the clock gene Per2 and clock-controlled genes of vascular endothelial growth factor (VEGF), Ki67, c-Myc, and P53 in different stages of carcinogenesis in buccal mucosa carcinoma and their roles in the development of buccal mucosa carcinoma. Methods  Ninety Syrian golden hamsters were housed under 12 h light/12 h dark cycles. Dimethylbenzanthracene (DMBA) was used to establish the carcinoma model by smearing the golden hamster buccal mucosa. Before DMBA painting and after 6 and 14 weeks, the hamsters were sacrificed at six time points within a period of 24 h (i.e., 4, 8, 12, 16, 20, and 24 h after light onset), and the normal buccal mucosa, precancerous lesions, and cancer tissues were simultaneously obtained. Hematoxylin and eosin stained sections were prepared to observe the canceration of each tissue. Real time polymerase chain reaction was used to detect the mRNA expression of Per2, VEGF, Ki67, c-Myc, and P53. Cosine analysis was employed to determine the circadian-rhythm variations of Per2, VEGF, Ki67, c-Myc, and P53 mRNA expression in terms of median, amplitude, and acrophase. Results  The expression of Per2, VEGF, P53, and c-Myc mRNA in three different stages appeared with circadian rhythms (P<0.05), whereas the Ki67 mRNA was expressed with circadian rhythm only in normal and precancerous lesion stages (P<0.05). The midline-estimating statistic of rhythms (MESORs) of Per2 and P53 mRNA were significantly down-regulated with the development of cancer (P<0.05), whereas the MESORs of VEGF, c-Myc, and Ki67 mRNA were up-regulated (P<0.05). The amplitude of P53 mRNA significantly decreased with the development of cancer (P<0.05). Moreover, compared with the normal group, the amplitudes of Per2, VEGF, Ki67, and c-Myc mRNA significantly increased in precancerous lesions and cancer tissue (P<0.05). In precancerous stage, the acrophases of Per2, VEGF, and c-Myc mRNA were earlier than that in the normal group, whereas that of Ki67 and P53 mRNA were delayed. Conclusion  The circadian-rhythm characteristics of the clock gene Per2 and clock-controlled gene expression of VEGF, Ki67, c-Myc, and P53 mRNA have changed with the occurrence and development of carcinoma.

Key words: clock gene Per2, clock controlled gene, circadian rhythm, oral cavity, carcinoma